<p>Yeah…just looking over practice problems for contest tomorrow.</p>
<p>these are like alg 2/pre-calc though</p>
<p>can you help quickly</p>
<li><p>Find the focus of the parabola y^2=-36 x
A (9,0)
B (-9,0)
C (0,9)
D (0,-9)</p></li>
<li><p>Find the period of 8sin(7x). </p></li>
<li><p>Find the equation of the ellipse with center (-9,3) and vertex (0,3) and a minor axis of length 10.</p></li>
</ol>
<p>These are just things I totally forget, but if you can help I’d love it.</p>
<p>biz-ump up</p>
<p>1) A</p>
<p>2) 2pi/7</p>
<p>3) (x+9)²/81 + (y-3)²/25 = 1</p>
<p>Can you review for me how to get 2 and 3. You answered number 1 incorrectly, but the other 2 were right if you could please show me.</p>
<p>last bump...</p>
<ol>
<li><p>B - parabola opens to the left. Focus is p away from vertex (0,0). So, -1/36 y^2 = x. -1/36 = 1/4p, p=-9 Focus is (-9,0).</p></li>
<li><p>The 7 changes the period from 2pi to 2pi/7 because the 7 affects the curve as a horizontal compression by a factor of 1/7.</p></li>
<li><p>Ellipse with horiz major axis is ((x-h)^2)/a^2 + ((y-k)^2)/b^2 = 1. a=1/2 of major axis, b=1/2 minor axis so (x+9)^2/81 + (y-3)^2/25 = 1.</p></li>
</ol>
<p>Okay, it's all coming back to me. Thanks!</p>
<p>Good luck!</p>
<p>Right, my bad. Was thinking of the determinex.</p>